Natural-Philosophical Collections: 309 
On the mode of Formation of certain Mineral Substances, by M. Becquerel.— 
The surprising progress which geology has latterly made, has been the means of 
our arriving at satisfactory knowledge, as well on the respective age of terrains, as 
on the mode of formation of the greatest part of them. But if we were almost 
agreed upon the question relative to the general mode of formation to which we 
must refer them, there was still much obscurity upon the processes by which na- 
ture has effected the composition of some of them. 
Many chemical compounds, indeed, which nature exhibits in the bosom of the 
earth cannot be reproduced in the laboratories of our chemists. There are others 
which artificial chemistry has been able to recompose, but which cannot be crys- 
tallized as they are found in nature. 
A blank, then, existed in this respect in the science, and it was of importance 
to have it filled. M. Becquerel, known by his numerous and important labours 
on electricity, seemed bound to supply it, and to furnish to geology the comple- 
tion of which she had need. It resulted from his researches, that it was the in- 
fluence of electrical forces, acting with inferior intensity in a continuous manner, 
which was wanting to the apparatus of our chemists to enable them to imitate the 
products of nature. — , 
M. Becquerel, in a memoir which he lately read before the Academy of Sciences 
of Paris, treated first of the crystallized metallic sulphurets, and Ueno ea with 
the sulphuret of silver. 
The apparatus of which he makes use consists of two tubes of glass, open at 
both extremities, and filled at the inferior part with very fine clay, slightly moist- 
ened with a liquid conductor of electricity. In the superior part are poured li- 
quids whose action upon each other, and npon the plate of metal, which is 
plunged by one of its extremities into each of them, gives rise to the electrical ef- 
fects necessary to the production of compounds. The two tubes are placed in an- 
other which contains a liquid meant to establish a communication between them. 
To obtain the sulphuret of silver, a saturated solution of the nitrate of silver is 
poured into one of the tubes, and a solution equally saturated with the hydro- 
sulphate of potass into the other; and then the extremity of a plate of silver is 
immersed in each of them. That which is in contact with the nitrate becomes 
quickly coated with silver in a metallic state, whilst that, on the other hand, 
which is the positive pole, forms water and sulphuret of silver, which combines 
with the sulphuret of potassium. This double sulphuret is decomposed by de- 
grees by the action of the nitric acid, which only takes place latterly, because, in 
chemical decompositions produced by electrical forces of low intensity, the oxygen 
goes at first alone to the positive pole, and the acid not till afterwards. It forms 
sulphuret of potassa; the sulphuret of silver is separated and crystallizes in beau- 
tiful little octahedral crystals, whose aspect is similar to that of the crystals of 
the same substance as found in the mines of silver. 
The crystallization of the sulphuret of silver is owing to a very aoe decompo- 
sition of the double sulphuret, which gives time to the molecules to effect the os- 
cillatory movement necessary to allow the similar faces to act upon each other, 
by virtue of the laws of crystallization. 
The sulphuret of copper is obtained by the same process, and it is in every re- 
-spect similar to the native sulphuret. 
The oxy-sulphuret of antimony or kermes is produced in the same manner. 
It is obtained in small octahedral crystals of a deep brown-red colour, or in cry- 
stallized plates. 
It is probable that the sulphurets of lead, of tin, and of mercury, may be ob- 
_tained by a similar process. 
* With the sulphurets of iron and of zinc, which decompose easily by the simul- 
taneous contact of water and air, it is necessary to employ certain precautions to 
prevent this decomposition. M. Becquerel has obtained very small cubic crystals 
of sulphuret of iron of a yellow colour, similar to that of pyrites. 
_ He concludes, fi from the results at which he has arrived, that it is probable he 
